Yes this was an April fools, sorry. A straight HDMI cable from your Genesis/Mega Drive is impossible without the use of some kind of up-scalling unit like the XRGB mini Framemesiter. There are other HDMI converters out there, but be aware of cheap converters available from Ebay and Amazon which may not support RGB video, only composite video (CVBS). I wrote an article on what converters to avoid here after receiving a lot of bad feedback from gamers who had purchased one of these cheap units. So in reality to play your Sega Genesis on a HDMI TV you will need an RGB SCART cable in-conjunction with a decent HDMI converter, like the Framemeister XRGB-mini or Open Source Scan Converter (OSSC).
HYPER 8K READY! Com'on Guys, this should have given the game away!